A seal for a coupling element which is conducted out of the inside of a cylinder, such as, for example, a piston rod or a pull belt of a work cylinder operated by pressure fluid (either liquid or gas), is subject to particular mechanical stresses. The seal must sufficiently seal the inside of the cylinder in view of the friction exerted by the piston rod or the pull belt during its axial movement. Federal Republic of German Patent OS 39 14 889 discloses a seal for work cylinders provided with a pull belt. Such cylinders are known as piston-rodless work cylinders. In that piston-rodless work cylinder, the receiving chambers for the sealing elements are in the cylinder covers, and the pull belt is conducted through the sealing elements in sealed fashion out of the inside of the cylinder. In that design, the pull belt is a flat steel tape. Typically, such steel tapes are sealed off at the two inside ends of the cylinder and, outside of the cylinder, are deflected by deflection rolls parallel to the cylinder and attached to a force-applying carriage which is guided along the length of the outer surface of the cylinder. The seals at the ends of the cylinder are each comprised of two sealing elements which form the seal upon being united and inserted into the corresponding receiving chambers in the cylinder covers. Each of the seal halves or seal elements has a sealing lip which, when joined, rests on the pull belt opposite each other transverse to the direction of movement, or longitudinal axis, of the pull belt. The pull belt, which is a steel tape, is thin so that it is flexible and can wrap around the deflection rolls. Nevertheless, in the case of traditional pull belts, the sealing lips are not applied optimally in the region of the edge, and, as a result, leaks occur in these regions. Also, the edges of the pull belts can be so sharp that they cut into the sealing lips when the pull belt shifts laterally during its movement thereby eliminating the sealing action within this region.
Federal Republic of German Patent Document AS 1,293,037 discloses a seal for use with a steel tape as pulling means in which bar-shaped elastic elements are provided as a seal for the pulling means. The elastic elements are positioned in the cylinder covers transverse to the longitudinal axis of the pull belt. These elastic cylindrical elements are made so that they exert mechanical stress against the cylinder covers and thus apply themselves against the steel tape.
Although sealing lips could be eliminated because the elastic elements have a round cross section, this seal, like the above-mentioned seals, does not provide a sufficient seal in the narrow-edge region proximate to the steel tape or pull belt.
If pull means are used that have a cross-sectional shape that differs from the known "steel tape", then known seals can no longer be used.
European Patent Document 0 384 032 discloses a pull means having a cross sectional shape that differs from circular or from the typical steel-tape shape. Instead, a pull belt having an oval cross-sectional shape, among others, is disclosed. The pull belt is formed of a flexible plastic material which is internally reinforced by, for example, embedded pull strands. Such a pull means, as already stated, cannot be sealed with traditional seals.